The beloved transmutes faults into virtues; the speaker's love consists of urging restraint, not in using beauty's destructive power.
Sonnet 96 continues the theme of beauty's destructive potential but adds a conditional about love itself. The speaker loves the beloved partly because the beloved chooses restraint—the beloved could seduce 'lambs' by appearing innocent, could lead 'gazers' astray through sheer magnetism, yet doesn't. Love, in this sonnet, consists of admiring power held in check. The speaker's claim 'As thou being mine, mine is thy good report' suggests his love depends on the beloved's continued restraint, not on absolute devotion.
The paradoxical final couplet means: the speaker owns the beloved precisely because the beloved doesn't exercise power. If the beloved began using their full potential, the ownership would evaporate. Love here is contingent on the beloved's self-limitation. The speaker doesn't love the beloved absolutely; he loves the beloved's choice not to be fully themselves. This is love as mutual constraint, with the speaker's ownership purchased by the beloved's voluntary dimming of their own brilliance.
You date someone stunning who could emotionally wreck people if they tried. You know this. But you love them partly because they choose not to—because they're kind despite having the power to be cruel. Your whole relationship depends on them never actually using their full potential.